– The font rendering works better for my eyesight.
– Killer feature: Ctrl+N/K clones the browser window/tab including the history. I.e. you can effectively fork the history. EDIT: And, equally important, opening a link in a new tab/window also preserves (clones) the history.
– Certain keyboard operations have better usability than on other browsers.
– The title bar + address/tab bar height height is smallest among all browsers (after some configuration).
I’m slowly getting used to the inevitability of migrating to Firefox. The font rendering and especially the clone-by-keyboard feature are the hardest part though. (And the fact that Firefox doesn’t allow yellow as a search highlight color.)